Luna’s comments to EW will undoubtedly come as a disappointment to S.H.I.E.L.D. fans who grew to love having him around in the first leg of Season 4, and his reappearance later in the season felt like a sign that maybe S.H.I.E.L.D. could find a way to bring him back on a regular basis.
After all, he was central to a major arc and had powers that could help the agents out significantly.
However the 100th episode of Agents of S.H.I.E.L.D. answers the question of what deal Coulson made with the Spirit of Vengeance, it won’t involve any new scenes with Gabriel Luna as Robbie Reyes.